It’s not the school - it’s the “parents”.
Our kids went to very liberal public schools growing up. At dinner time we would discuss things and have various learning experiences on what they had been taught. All three are still staunch conservatives. I think them being taught all of the liberal crap when they were young helped us to educate them so they wouldn’t get sucked into it when they went off to college.
And of course it wasn’t just talks at the dinner table but showing them by our actions as well.